With the ever-increasing oil price, fuel economic efficiency and fuel-saving potentials of an engine are becoming more and more important. Recently, most fuel-saving researches are focused upon developing variable valve actuation mechanism since it is the foundation of various fuel-saving techniques, such as cylinder deactivation, engine down-sizing, and so on.
Currently, there are various researches relates to valve lift control. One such research is disclosed in U.S. Pat. No. 6,223,706 B1, as that illustrated in FIG. 1. As seen in FIG. 1, the variable valve actuation mechanism 1 is basically a hollow outer annular part 10 concentrically enclosing an inner annular part 11, whereas the two parts 10, 11 are axially movable relative to each other. Cams of different lift (not shown) are arranged for enabling the same to have contact with the outer and inner annular parts 10, 11 in respective, and the switching between different valve lifts is controlled by a locking means. The locking means is comprised of three slides 12, 13, 14, which are arranged and extending in receptions 101, 102, 103 respectively formed in the outer and inner annular parts 10, 11, and are capable being forced by a hydraulic means and inset into recesses of the outer and inner annular parts 10, 11 in respective for separating or coupling the two annular parts 10, 11.
As the three slides 12, 13, 14 are held at a specific position by the resilience of a spring 15,17 as seen in FIG. 1, the outer and the inner annular parts 10, 11 are separated. However, while intending to couple the two annular parts 10, 11, the hydraulic means is activated for pushing the slide 14 and thus forcing the same to enter the reception 102 of the inner annular part 11. Therefore, by the separating/coupling of the two annular parts 10, 11, various valve lifts can be enabled. However, it is noted that if the three slides 12, 13, 14 are not perfectly aligned and thus the slide 14 can be pushed to enter the reception 102 accurately and smoothly, the switching of valve lift will fail.
In addition, when a low lift is selected and the low-lift cam is pressing upon the inner annular part 11 for thus actuating the corresponding valves of an engine, the high-lift cam that is not selected will still press upon the outer annular part 10. Although the displacement of the outer annular part 10 is absorbed by a spring 16 arranged inside the outer annular part 10, it will still have affect upon the valves of low loft whenever there is a situation that the spring 16 is poorly designed or a force is maintained upon the spring 16 while the high-lift cam is pressing upon the outer annular part 10.
Therefore, it is in need of a variable valve actuation mechanism that can free from aforesaid drawbacks.